Methicillin (USAN) or meticillin (INN, BAN) is a narrow spectrum beta-lactam antibiotic of the penicillin class. It was developed by Beecham in 1959. It was previously used to treat infections caused by susceptible Gram-positive bacteria, particularly beta-lactamase-producing organisms such as Staphylococcus aureus that would otherwise be resistant to most penicillins, but is no longer clinically used. Its role in therapy has been largely replaced by flucloxacillin and dicloxacillin, however the term methicillin-resistant Staphylococcus aureus (MRSA) continues to be used to describe Staphylococcus aureus strains resistant to all penicillins. Meticillin is no longer in manufacture as the more stable and similar penicillins; oxacillin (used for clinical antimicrobial susceptibility testing), flucloxacillin and dicloxacillin are used medically.